The present invention relates to a pipe intended to be installed in position in a body of water from a surface that is subjected to a variation in height, the pipe extending between a surface end and a bottom end, and defining an internal passage ending at the bottom end and at the surface end, the pipe comprising a dynamic closing member at the bottom end which is adapted so as to open above a threshold pressure, applied from the exterior towards the interior of the pipe and to close below the threshold pressure.
The pipe is in particular a corrosion resistant pipeline.
It is a known practice to use a pipe whose internal surface is made of a corrosion-resistant alloy, the pipe is then referred to as a CRA pipe. CRA is an acronym for “Corrosion Resistive Alloy”, as per accepted terminology. There are different types of CRA pipes. The SDPs “Super Duplex pipelines” are manufactured out of a single alloy that is corrosion resistant. The MCPs “Metallurgically clad pipelines” are pipes whose internal surface is covered with a corrosion-resistant alloy by means of a surface treatment process. The MLPs “Mechanically lined pipelines’ are pipes which have an internal jacket manufactured out of a corrosion resistant alloy. The MLPs are sometimes also known as “clad pipelines”. The CRA pipes may also be obtained by other means of fabrication
It is known practice to use other types of corrosion resistant pipes, in particular, PLP pipes. PLP is the acronym for “Plastic Lined Pipe”, for pipes having a plastic coating.
In deep water, the weight of a pipe to be laid becomes a problem on account of the limited capacities of the pipe laying equipment.
The laying of empty pipes makes it possible to limit this weight problem. But such pipe laying is difficult for several reasons. Empty pipes are not resistant to the hydrostatic pressure below a certain depth. In addition, the weight of the pipe may be useful for stabilising the pipe on the bottom or bed of the body of water during the laying operations. Indeed, the lighter the pipe, the more sensitive it is to the currents and thus has a tendency to move in the currents.
One solution is to lay a pipe that is only partially empty. When the pipe is empty up to a certain depth, it is much easier to handle and manipulate.
It is therefore necessary to control the weight of the pipe by controlling the height of the water column within the interior of the pipe.
It is a known practice to employ passive immersion units, that is to say “passive flooding unites” PFUs in order to inhibit and filter the sea water entering the pipe so as to limit corrosion. An inspection valve upstream or downstream of the PFU provides the ability to control whether or not to trigger the flooding of the pipe in a passive manner.
However, during the laying of a pipe that is partially filled from a floating surface, for example, from a pipe laying vessel, the floating surface is subjected to a variation in height. The height variation of the surface results in the moving of the pipe.
The water within the pipe is not stationary by virtue of its fluid nature. Thus when the pipe commences its dynamic movement, the water is driven by the movement of the pipe. Quickly, the free water within the interior of the pipe is driven by its inertia. The water then begins an alternating translational movement in relation to the pipe.
This dynamic movement of water that is unsynchronised with the movement of the pipe is amplified by the compressibility of the water and the pipe that may be expandable, in particular in the direction of its diameter, under the force generated by the moving water column. This complex dynamic movement may generate a standing acoustic wave.
This dynamic movement consequently has the effect of expelling the water inside the pipe through the end of the pipe located on the pipe laying vessel up to the level of the deck or beyond.
The dynamic movement of the water within the pipe is referred to as heave. Heave is a translational movement from top to bottom.
The expulsion of water due to the heave is dangerous for the people located on the pipe laying vessel. In addition, the water expelled by the heave represents the risk of damaging the equipment and materials present on the pipe laying vessel.
In addition, the heave adds complexity to the operations related to assembly or welding of the sections of the pipe on the pipe laying vessel. Similarly, the heave also renders difficult the assembly of a pipe section having a sub-sea architecture such as an ILT (In Line Tee) architecture, an FLET (Flowline End Termination) architecture or others.
Indeed, it is important to maintain the surface of the water within the interior of the pipe at a distance from the upper end of the pipe, in a manner so as to limit the humidity and the discharges of chemical products during the welding operations. The welding is particularly complex in the case of CRA pipes. Similarly, the assembly of connectors of the sections of a flexible pipe is impacted by the level of the water.
An alternative method for fabricating and laying of pipes is based on the insertion of a plug into the pipe. The insertion of a plug is, for example, used in order to avoid the expulsion of water by the end of the pipe during welding operations. However, this operation is long and laborious. It is additionally also necessary to remove the plug at the end of the installation process in order to use the pipe.